As in other fields of technology, integrated circuits are being used more widely in automobile technology, for example in the form of microprocessors or microcontrollers. Devices for supplying power are provided to enable their operation. Known devices of this type commonly contain an external blocking capacity which is connected in parallel between a supply input of the integrated circuit and earth, and a voltage source which is connected in parallel to it. The voltage source charges the isolating capacity, and the power which is fed to the integrated circuit is removed from the isolating capacity by means of a discharging current. This is designed to achieve the most realistic simulation possible of an ideal voltage source. The known devices for supply power lead however to an unwanted high level of radiation of electro-magnetic energy, in particular when a clocking frequency of the integrated circuit becomes greater than 10 MHz. Then, the EMC standards set by the automobile industry are also potentially no longer met. cl SUMMARY OF THE INVENTION
For this reason, the object of the invention is to provide a device of the type described in the introduction, with the aid of which an integrated circuit can be supplied with power even with a high clocking rate, in particular in the MHz range, whereby at the same time, the EMC standards set by the automobile industry are maintained.
In order to attain this object, the invention provides a device for supplying power to a rapidly clocking, integrated circuit, which comprises a circuit load to be supplied with the power and an internal capacity, which is connected parallel to the circuit load, wherein the device has the following features. The integrated circuit has a high clocking frequency, which is in particular at least in the MHz range. A supply unit, which is in particular designed as a current source, is directly connected to the internal capacity. The supply unit has an internal resistance, the impedance value of which is so high at the clocking frequency and in particular with its harmonics, that a current, which supplies the circuit load, originates to a greater degree from the internal capacity than from the supply unit. This device preferably benefits from the following two advantageous measures. On the one hand, no use is made of the external circuit with the additional isolation or blocking capacity. Instead, an internal bus capacity is used which is already available within the integrated circuit. On the other hand, instead of the low-ohmic voltage source which is used with the known devices, an energy supply is used with the highest possible internal resistance.
The combination of both measures decouples the frequencies when the bus capacity is charged and discharged. While the bus capacity continues to be discharged with the high clocking frequency, the charging is completed with a significantly lower frequency. The latter results from the low pass behavior of the combination of the bus capacity and the high-ohmic internal resistance of the supply unit. Charging frequencies which occur in connection with the charging are smaller by at least one order of magnitude than the discharging frequencies which occur in connection with the discharging, which are essentially determined by the fundamental wave (=clocking frequency) of the clocking rate of the integrated circuit and its harmonic waves. Incidental interferences arise as a result of the internal communication, the fundamental frequency of which is usually operated with half the clocking rate. Signal portions with the high-frequency discharging frequencies are closely restricted in terms of space, and essentially only lie within the integrated circuit. By contrast, signal portions with the low-frequency charging frequencies also run through a circuit board, onto which the integrated circuit is mounted. Neither of the signal portions creates a significant level of radiation of electromagnetic energy—the discharging signal portion due to the close restriction in terms of space within the integrated circuit, and the charging signal portion due to the low frequency.
Overall, an integrated circuit can therefore be supplied with electric power with a high clocking rate by means of the device according to the invention without a notable radiation of electromagnetic energy occurring. The EMC standards set by the automobile industry are also maintained, even with clocking frequencies in the upper MHz range.
A particular preferred embodiment is easy to realize, wherein the supply unit comprises a serial connection, consisting of a voltage source and the internal resistance, which acts as the current source. A current source, which is ideally characterized by an infinitely high internal or inner resistance, is simulated by means of a serial connection of a low-ohmic voltage source with the inner or internal resistance which is dimensioned in relation to the field of application. A voltage source can be constructed in a simple manner. This also applies in particular to a voltage-controlled voltage source.
In another embodiment, the supply unit is part of a regulating unit adapted to regulate the power supplied by the supply unit to the integrated circuit. This ensures that the energy feed corresponds to the current requirements.
In a further embodiment, the regulating unit further comprises a low pass, which is connected to the internal capacity in order to record a voltage that drops across the circuit load. This guarantees that the regulating unit comprises an advantageously low regulating speed. Thanks to the low pass effect, abrupt changes to the drop in voltage on the internal capacity only lead to a slow simulation of charging power.
In a variant, the supply of the power by the supply unit exhibits a low pass behavior with a transition frequency that is lower than the clocking frequency. This prevents high-frequency signal portions from also occurring to a notable degree outside the integrated circuit, i.e. on the in and out or feed and return conductor lines on the circuit board, where they can lead to radiation.
According to another embodiment, the internal resistance comprises a series circuit of at least one low-capacity resistance and a ferrite element. This prevents a too strong inF1uence of the parallel capacities of the individual elements used to realize the internal or inner resistance. Parallel capacities are unfavorable because they comprise a low impedance value at high frequencies. The serial connection of a resistance and a ferrite element reduces the unwanted inF1uence of the parallel capacity of the ferrite element. Equally, the inF1uence of the parasitic parallel capacity of the resistance is reduced when several resistances are connected in series. A good compromise between expense and useful benefit is achieved in particular by the serial connection of four low-capacity resistances. The at least one low-capacity resistance reduces the bridging capacity of the overall arrangement and provides an effective fundamental attenuation, in contrast to which the ferrite element has an unwanted high level of loss, precisely in the high clocking frequency range.
The advantageous further embodiments described below can be realized in any combination required.